The present invention relates to a current clamp. More specifically, the present invention relates to detecting closure of jaws on a current clamp.
A current clamp (also known as a current probe or amp clamp) is an electrical device that has a pair of jaws, which, when closed, form a closed curve (such as a circle or oval). When the jaws are closed around an electrical conductor, properties of the electric current flowing in the conductor can be measured, without requiring physical contact with the conductor or disconnection of the conductor for insertion through the probe. Current clamps can be used to read the magnitude of an alternating current. Also, in conjunction with more advanced instrumentation, the phase and wave form of the current can be detected as well.
One type of current clamp comprises a split ring of ferrite or soft iron. The split ring is split into two halves, each of which have a wire coil wound therearound. The wire coil forms one winding of a current transformer. When the current clamp is placed around a conductor, the conductor forms the other winding.
Another type of current clamp is referred to as an iron vane clamp. In this type of current clamp, the magnetic flux in the core directly affects a moving iron vane that allows both A/C and D/C current to be measured. It also gives a true RMS value for non-sinusoidal A/C wave forms.
Yet another type of clamp, with a meter, is referred to as a Hall Effect meter. This type of meter is more sensitive and is able to measure both D/C and A/C current. Normally, a current clamp only works when it is placed around one conductor of a circuit under test. The reason is that if it is placed around both conductors, the magnetic fields cancel.
When the current clamp is integrally combined with an electrical meter, the device is known as a clamp meter (and is also sometimes referred to as a clamp-on ammeter or tong tester). Clamp meters can also be used to measure electrical power and energy. The clamp is used to measure the current and other circuitry measures the voltage. The true power is the product of the instantaneous voltage and current integrated over a cycle.
The accuracy of each of these devices can be affected if the jaws do not fully close around the conductor. When this occurs, the magnetic loop is not continuous, and the meter reading associated with the current clamp is erroneous (and usually too low).